The present invention relates to devices for operating the gear change of a bicycle, of the type comprising
a main body rotatably mounted on a support pin and provided with an operating lever which is resiliently biassed towards one of its end positions,
a member driven by the main body and rotatably mounted on the support pin,
friction coupling means operatively interposed between the driven member and the support pin for opposing rotation of the driven member by means of frictional resistance, and
one-way engagement means operatively interposed between the main body and the driven member for coupling the driven member to the main body for rotation only when the operating lever is rotated towards the said end position.
In devices of the type specified above, the main body of the device is connected to the rear derailer of the bicycle by means of a Bowden cable. The derailer includes a spring which tends to urge the operating lever towards the position corresponding to engagement of the bicycle chain with the smallest-diameter sprocket carried by the rear wheel of the bicycle. When the lever is released in a position other than the above position, movement of the lever due to the biassing of the derailer spring is prevented by the friction generated by the friction coupling means. When the operator operates the lever, moving it towards to end position, he has to overcome this friction and is assisted in this operation by the derailer spring. When the operator needs to move the lever away from the end position, however, he only has to overcome the reaction of the derailer spring, since the one-way engagement means enable the main body of the device to rotate freely relative to the driven member. In this way, the force which has to be applied by the cyclist to the operating lever remains substantially unaltered, whatever the direction of movement of the lever.
An operating device of the type indicated at the beginning of the present description is described and illustrated in U.S. Pat. No. 3,693,469. In this known solution, the one-way engagement means are constituted by a ratchet gear comprising a pawl carried by the main body of the operating lever and a toothed wheel which itself constitutes the driven member of the device. This known solution, however, is not always completely satisfactory in use. Other devices of the type indicated above have also been suggested, but have the disadvantage of being relatively complicated, or of requiring manufacture to very low tolerances, or even of enabling engagement only in a fixed number of positions.